The present invention relates generally to semiconductor fabrication, and relates more specifically to photolithographic techniques for fabricating semiconductors.
The present invention relates generally to semiconductor fabrication, and relates more specifically to photolithographic techniques for fabricating semiconductors.
Defect growth during exposure is a growing concern in the photomask industry. Surface contaminants from the mask manufacturing process, outgassing from pellicle, adhesives, and storage containers, as well as general airborne contaminations can react during lithographic exposure and form defects on both the frontside (sub-pellicle) and backside of the mask. Sub-pellicle defect growth is a growing concern because the defects are in the focal plane of the mask and can actually print onto the semiconductor wafer. Although backside defects are not in the focal plane, they are also a concern because a large number of defects can cause a “haze” that affects the transmission of light through the mask. In addition, residual metals and other impurities on the frontside and backside of the mask may act as nucleation sites for defect growth, because these defects are often composed of heteroatoms that are very reactive with metals. It is often found that defects are formed from contaminants containing heteroatoms that are very reactive with metals and other inorganic impurities.
Conventional methods for reducing mask surface contamination include the application of fluorocarbon films that require specific tooling, or the application of aqueous solutions that prevent large crystal formation but do not prevent backside haze.
Thus, there is a need in the art for a method and apparatus for sub-pellicle defect reduction on photomasks.